In modern days, many devices require remote interaction with spatially distributed objects for a number of applications. For example, remote detection of high-resolution imagery, by means of cameras, is indispensable for social media, artificial-intelligence systems, self-driving cars, security tools, and so on. However, light cannot penetrate opaque obstacles, and it can be easily disturbed by fog and rain, or scattered by textured surfaces, or absorbed by black substances, potentially leading to unexpected events or even fatal accidents. On the other hand, conventional radio-frequency (RF) technologies can resolve the aforementioned problems, but the component size is typically large, preventing widespread application of RF technologies in imaging, detection, dense wireless communication networks, etc. Recently, the rapid advancement of high-frequency mm-wave and THz (Tera-Hertz) technologies makes the RF apparatus of smaller form factor be practical of monitoring, sensing, and communicating with objects distributed over a large space simultaneously, thereby resolving most of the issues associated with light-wave apparatus at lower and affordable cost. For another example, future wireless base station calls for complicated, dense, and user-scaling RF communication technology to trace numerous mobile devices dynamically so that their communications with the base station are stable. However, such complexity inevitably leads to both high power consumption and high cost, bringing great pressure on RF communication equipment providers.
There are at least two main candidate electromagnetic (EM) solutions known to date for a local device to interact with remote objects electronically: the first is the phased array system and the second is the lens-based image array system. Here briefly mentions the operation principle of the phased array system: numerous phase-shifting elements are arranged as an array, and the phase of each element is adjusted such that the EM waves (electromagnetic waves) emitted from (received by) all the elements are synthesized into a focused EM beam pointing to (or receiving from) a specific direction. This allows searching or delivering signals in the form of EM waves through different space channels to the remote objects of interest. Next is the brief summary of the operation principle of the lens-based image array system: a lens set is positioned in front of a pixel array, and each pixel consists of an EM wave receiver, so that any EM wave transmitted from the objects may be collected by the lens and then processed by a detector located at a specific position on the focal plane of the lens set. Furthermore, the optical properties of the lens-based image array system may be adjusted by interchanging the lens set (e.g. lenses with different field of views (FOV) and/or other optical properties that may be used independently).
All currently available technologies, however, still have obvious disadvantages. For example, the phased array system requires large and continuous computing power to synthesize the EM waves for beam steering and searching, which results in waste of computing time and energy. In addition, when moving to a higher bandwidth system that requires higher carrier frequencies, the phased array technology becomes increasingly complex because a large amount of high-frequency components such as antennas and phase shifters with sophisticated control scheme and calibrations are required, making the frequency scaling of phased array technology increasingly difficult. Even worse, the phase shifters in general not only requires control power, but also induces extra EM wave losses, nonlinearities (both in terms of power and frequency), and noise. On the other hand, state-of-the-art lens-based image array system only focuses on the EM wave reflected from the spatially distributed objects and through the passive lens set onto different locations in the focal plane, just like a traditional light-wave camera, which does not require any active components and algorithms for beam steering. [Refer to P. F. Goldsmith, C. T. Hsieh, G. R. Huguenin, J. Kapitzky, and E. L. Moore, “Focal Plane Imaging Systems for Millmeter Wavelengths” IEEE Transactions on Microwave Theory and Techniques, Vol. 41, No. 10, p. 1664-1675 (1993)]. The lens focusing property had been also used as an imaging antenna for automotive radars, utilizing a hemispherical lens with a backside reflector nearby the focal plane to generate a scanning multibeam radiation pattern by arranging an endfire tapered slot antenna array positioned in a circular arc surrounding the hemispherical lens. [Refer to B. Schoenlinner, and G. M. Rebeiz, “Compact Multibeam Imaging Antenna for Automotive Radars,” IEEE MTT-s Digest, p. 1373-1376 (2002)]. [Refer to U.S. Pat. No. 7,994,996 B2: “MULTIBEAM ANTENNA,” Inventors: Gabriel Rebeiz, James P. Ebling, and Bernhard Schoenlinner.] The microwave, millimeter-wave, and THz imaging array systems typically need high-power sources to obtain sufficient SNR (signal to noise ratio) to achieve the image quality close to the level of lightwave camera, despite that all the lightwave camera do not need any active components and algorithms for beam steering. Recently, the lens focusing properties were also adapted to the beamspace MIMO (maximum input maximum output) communication, which consists of discrete lens array (DLA) made of several laminated, planar surfaces patterned with sub-wavelength, bandpass, frequency-selective, phase shifters, thus constituting a continuous-aperture-phased artificial lens system of antenna (aperture) size A of spatial signal space dimension, n=4A/lambda2 (lambda is the free-space wavelength of the operating frequency.) The antenna aperture was coupled to p transceivers (p<<n) with p antenna feeds mounted on the focal plane, through which the MIMO algorithms controlled and steered the transmitted or received beams. The lens-based beam space MIMO still necessitated extensive signal processing power to cope with practical point-to-point and point-to-multi-point scenarios. [Refer to U.S. Pat. No. 8,811,511 B2: “HYBRID ANALOG-DIGITAL PHASED MIMO TRANSCEIVER SYSTEM,” Inventors: Akbar M. Sayeed, Madison, Wis. (US); Nader Behdad, Madison, Wis. (US)] [Refer to J. Brady, N. Behdad, and A. M. Sayeed, “Beamspace MIMO for Millimeter-wave Communications: System Architecture, Modeling, Analysis, and Measurements”, IEEE Transactions of Antennas and d Propagation, Vol. 61, No. 7, p. 3814-3827 (2013)].
Accordingly, it is desired to develop new technology for providing efficient remote object interaction, such as imaging, detection, communication, or other applications.